<!DOCTYPE html>
<html>
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Symbol 类型</title>
</head>
<body>
  <script>
    let genericSymbol = Symbol();
    console.log(genericSymbol);  // Symbol()

    let fooSymbol = Symbol('foo');
    console.log(fooSymbol);  // Symbol(foo)
  </script>
</body>
</html>